Boston Marathon bombing suspects

This image released by the FBI on Thursday, April 18, 2013, shows in a image from video what the FBI is calling suspect number 1 with a black hat walking with a backpack in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. (AP Photo/FBI)

This image released by the FBI on Thursday, April 18, 2013, shows in a image from video what the FBI is calling suspect number 2 with a white hat, highlighted, walking in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. (AP Photo/FBI)

This image released by the FBI on Thursday, April 18, 2013, shows in a image from video what the FBI are calling suspect number 1, front, in black cap, and suspect number 2, in white cap, back right, walking near each other through the crowd in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. (AP Photo/FBI)

This image released by the FBI on Thursday, April 18, 2013, shows in a image from video what the FBI is calling suspect number 2, highlighted, with a white hat walking in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. (AP Photo/FBI)

This image taken from video released by the FBI on Thursday, April 18, 2013 shows what the FBI are calling suspect number 1, front, in black cap, and suspect number 2, in white cap, back right, walking near each other through the crowd in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. (AP Photo/FBI)

Photos of two suspects sought in the Boston Marathon bombing are displayed during a news conference talking about the investigation of the Boston Marathon explosions, Thursday, April 18, 2013, in Boston. The city continues to cope following Monday's explosions near the finish line of the marathon. (AP Photo/Julio Cortez)

This image released by the FBI on Thursday, April 18, 2013, shows in a image from video what the FBI is calling suspect number 2, highlighted, with a white hat walking in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. (AP Photo/FBI)

This image released by the FBI on Thursday, April 18, 2013, shows in a image from video what the FBI is calling suspect number 1 with a black hat walking with a backpack in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. (AP Photo/FBI)

Photos of one of two suspects sought in the Boston Marathon bombing.

Associated Press

Special Agent in Charge of the FBIís Boston Field Office Richard DesLauriers addresses the media during a news conference talking about the investigation of the Boston Marathon explosions, Thursday, April 18, 2013, in Boston. The city continues to cope following Monday's explosions near the finish line of the marathon. (AP Photo/Julio Cortez)